Bond magnet and manufacturing method thereof, and actuator therewith

ABSTRACT

A bond magnet comprises a molded body in which a mixture of flake of magnet material comprising rare earth element-iron-nitrogen as main component, TbCu 7  type crystal phase as a principal phase and a thickness of less than 200 μm a binder is compression molded. A compression molded body constituting a bond magnet has a density of 6×10 3  kg/m 3  or more. In the step of compression molding a mixture of magnet material and binder, pressure is applied a plurality of times, or pressure is applied while rotating a punch and die, or the binder is cured while applying pressure to obtain such a bond magnet with good reproducibility. Such a bond magnet has excellent magnetic properties and corrosion resistance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to bond magnets used as high performancepermanent magnets and manufacturing methods thereof, and actuatorstherewith such as motors.

2. Description of the Related Art

So far, as one kind of high performance permanent magnets rare earthsystem magnets such as Sm—Co system magnets and Nd—Fe—B system magnetsare well known. A large amount of Fe and Co in these magnets contributesto increase saturation magnetic flux density. The rare earth elementssuch as Nd and Sm, due to a behavior of 4f electrons in a crystal field,cause very large magnetic anisotropy. Thereby, coercive force isincreased.

The rare earth magnets of high performance are employed in electricalappliances mainly such as motors and measuring instruments. Recently, inorder to cope with demands for smaller sizes and lower prices of variouskinds of electrical appliances, permanent magnets of higher performanceare in demand. In particular, in medium driving spindle motors used inhard disk drives (HDDs), floppy disk drives (FDDs), CD-ROM drives andDVD drives and actuators for driving light pick-ups used in CD-ROMdrives and DVD-drives, in realizing smaller size and higher performance,further improved permanent magnet is in demand.

To the demands for permanent magnets such as described above, forinstance R—Zr—(Fe, Co)—N system magnet material (R: rare earth elements)of which principal phase is TbCu₇ type crystal structure is proposed(cf. Japanese Patent Laid-Open Application (KOKAI) No. HEI 6-172936 andothers). A permanent magnet using such magnet material is in general abond magnet constituted of for instance a molded body (compressionmolded body) that is obtained by compression-molding a mixture of magnetpowder and resin-based binder into a molded body. The mixture of themagnet powder and the resin-based binder is press-formed by use of apress machine of general use.

Magnetic performance of the bond magnet such as described above,residual magnetization and maximum magnetic energy product ((BH)_(max))in particular, is determined by magnetic properties of the magnetmaterial being used and density of the molded body (compression moldedbody) constituting the bond magnet. That is, when the magnet material ofequivalent performance being used, by increasing the density of themolded body, the bond magnet can be made higher performance. When thedensity of the molded body is increased to decrease voids,corrosion-resistance of the bond magnet is also expected to improve.

However, in a manufacturing method of the bond magnet therein anexisting general press forming is applied, there is a limit in animprovement of the density of the compression molded body consisting ofthe mixture of the magnet powder and the binder. In particular, as inthe magnet material of which principal phase is TbCu₇ type crystalphase, when flakes (or a ribbon) of magnet material obtained byquenching are used, during press forming, there occurs friction orspring back between magnet materials. Thereby, the compression-moldedbody is hindered from being densified. Accordingly, the bond magnet isin a situation difficult to further improve performance due to animprovement of the density of the molded body.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a bondmagnet in which a density of molded body of bond magnet is furtherincreased to improve magnetic properties such as the maximum magneticenergy product, further corrosion-resistance. Here, in the bond magnet,magnet material of which principal phase is TbCu₇ crystal phase is used.Another object of the present invention is to provide a manufacturingmethod of bond magnets that enable to increase the density of the moldedbody with ease and reproducibility. Still another object of the presentinvention is to provide an actuator that is, by using bond magnet havingthe aforementioned characteristics, made smaller in size and higher inperformance.

The present inventors studied hard to achieve the aforementionedobjects. As a result, it was found that in manufacturing a molded bodyby compression-molding a mixture of magnet material and binder, bycontrolling conditions of press forming and shape of the molded body,the density of the molded body can be further increased.

That is, at first pressing, the mixture of the magnet material and thebinder is low in fluidity to cause a large fluctuation in microscopicdensity. By contrast, when pressure is lowered once during compressionmolding, in the form of spring back the fluctuation of local residualstress is released. Simultaneously, microscopic movement of the magnetmaterial broken during compression and the binder occurs. When themixture in such a state is pressed again, the magnet material and thebinder move so as to more homogenize internal stress to result in adecrease of microscopic fluctuation of the density within the moldedbody. Based on these, since press power during the compression moldingcan be more effectively utilized, the voids in the molded body (bondmagnet) are decreased to enable to improve the density.

During compression molding, by applying pressure while rotating orreciprocating a forming mold such as a punch or a die, the density ofthe molded body also can be increased. Since rotary or reciprocatingmotion of the forming mold applies shearing stress or the like to themixture, the mixture is more positively forced to flow. Accordingly,further densification of the bond magnet can be realized. Further, bycuring the binder while applying pressure to the mixture, the bondmagnet can be more densified.

Further, by optimizing the shape of the molded body, the density of thebond magnet can be easily increased. For instance, a ring of the bondmagnet, by making appropriate a ratio of a thickness and a height of thering portion or the specific value of a thickness, the density of themolded body can be further increased with ease. For the bond magnetformed in disk or a rectangular plate, a reduction of the thickness toless than an appropriate value is effective.

The present invention is accomplished based on such knowledge. The bondmagnet of the present invention is one comprising a molded body in whichthe mixture containing magnet material of which main component is rareearth element-iron-nitrogen and a binder is formed into a magnet shape.The magnet material comprises TbCu₇ crystal phase as a principal phaseand a shape of flake of a thickness of less than 200 μm, the molded bodythereof having a density of 6×10³ kg/m³ (6g/cm³) or more. In the bondmagnet of the present invention, the density of the molded body ispreferable to exceeds 6.1×10³ kg/m³ (6.1 g/cm³).

The present invention, when as the flakes of magnet material one that isobtained by incorporating nitrogen in an alloy ribbon consisting of aquenched body of molten alloy is used and a thickness thereof is in therange of 5 to 50 μm, is particularly effective. The flakes of magnetmaterial are preferable to comprise TbCu₇ crystal phase of which averagegrain diameter is in the range of 5 nm or more and less than 50 nm as aprincipal phase. Thus, by employing the flakes of magnet material whichcomprises fine TbCu₇ crystal phase as a principal phase, magneticproperties of the bond magnet can be further improved.

In the present bond magnet, the kind of the binder is not particularlyrestricted. However, the present invention is particularly effective forthe bond magnet that uses resin-based binder. The content of theresin-based binder is preferable to be in the range of 0.5 to 5% by massto magnet material. The present bond magnet comprises acompression-molded body of the mixture of for instance the flakes ofmagnet material and the binder.

A first method for manufacturing the bond magnet of the presentinvention is one for manufacturing the bond magnet that comprises a stepof compression-molding a mixture of magnet material and binder into adesired magnet shape. In the step of compression molding, the pressureis applied to the aforementioned mixture a plurality of times.

The first method for manufacturing the bond magnet is characterized inthat in more specifically in the step of compression molding, between amaximum pressure and 90% or less thereof, compression and decompressionto the mixture are alternately repeated. Further, in the step ofcompression molding, a procedure comprising a step of applying thepressure of 6×10² MPa or more to the mixture and a step of releasing thepressure by decreasing the pressure by 2×10² MPa or more is preferablyrepeated twice or more.

A second method for manufacturing the bond magnet of the presentinvention is characterized in that, in the method for manufacturing thebond magnet comprising a step of compression molding the mixture of themagnet material and the binder into the desired magnet shape, in theaforementioned step of compression molding, while rotating orreciprocating at least one selected from a punch and die for compressionmolding, the pressure is applied to the mixture.

A third method for manufacturing the bond magnet is characterized inthat, in the method of manufacturing the bond magnet comprising a stepof compression molding the mixture of the magnet material and the binderinto the desired magnet shape, in the step of compression molding, whileapplying the pressure to the mixture, the binder is cured.

The present methods for manufacturing the bond magnets are particularlyeffective when the bond magnets are produced with flakes of magnetmaterial of which main component is rare earth element-iron-nitrogen andprincipal phase is TbCu₇ crystal phase as the magnet material and withresin-based binder as the binder. In addition, when a thickness of theflakes of magnet material is less than 200 μm, the present methods areeffective. The present manufacturing method is also applicable tomanufacture of bond magnets that employ other magnet material,contributing in increasing the density of the molded body. As the othermagnet material, for instance magnet materials comprising Th₂Ni₁₇crystal phase, Th₂Zn₁₇ crystal phase or R₂Fe₁₄B crystal phase (R: rareearth element such as Nd) as principal phase can be cited.

An actuator of the present invention comprises the bond aforementionedmagnet of the present invention. The present actuator described abovecomprises the present bond magnet for instance and means for operating amoving body with magnetic force of the bond magnet as driving force.Such actuators of the present invention are suitable for various kindsof actuators to which the smaller size and higher performance aredemanded. The suitable examples of actuators are medium driving spindlemotors used in HDDs, FDDs, CD-ROMs, DVDs and the like, motors forprinters, vibration generating pager motors of such as portabletelephones, lens actuators of optical pick-ups, actuators of automobilespeed meters, linear actuators, and various kinds of magnet rolls. Thebond magnets of the present invention also can be used as magnets forspeakers of higher sound quality and thinner thickness used in portabletelephones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one example of a shape suitable fora bond magnet of the present invention;

FIG. 2 is a cross section showing another example of a shape suitablefor a bond magnet of the present invention;

FIG. 3 is a diagram for explaining a first embodiment of a secondmanufacturing method of the present invention;

FIG. 4 is a diagram showing a modified example of the embodiment of themanufacturing method of the bond magnet shown in FIG. 3;

FIG. 5 is a diagram for explaining a second embodiment of the secondmanufacturing method of the present invention;

FIG. 6 is a diagram for explaining a third embodiment of the secondmanufacturing method of the present invention;

FIG. 7 is a diagram showing a modified example of the embodiment shownin FIG. 6;

FIG. 8 is a diagram for explaining a fourth embodiment of the secondmanufacturing method of the present invention;

FIG. 9 is a diagram of one example of constitution of a hard disk drive(HDD) that comprises a spindle motor using the bond magnet of thepresent invention as a medium driving motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, modes for implementing the present invention will beexplained.

A bond magnet of the present invention comprises a molded body(compression molded body) that is obtained by forming a mixture ofmagnet material and binder into a desired magnet shape. Here, the magnetmaterial comprises rare earth element-iron-nitrogen as main componentsand TbCu₇ type crystal phase as a principal phase. As the magnetmaterial, one in flakes of a thickness of less than 200 μm is used. Themolded body constituting such a bond magnet possesses a density of 6×10³kg/m³ or more.

In the bond magnet in which flakes of magnet material of which principalcrystal phase is TbCu₇ crystal phase and thickness is less than 200 μmare used, the density of 6×10³ kg/m³ or more can be realized withreproducibility through optimization of the shape of the molded body orcontrol of conditions during compression-molding. In the presentinvention, through the control of the press conditions, the bond magnetthat has the density of molded body of 6.1×10³kg/m³ or more can beobtained.

According to the bond magnet constituted of the aforementionedcompression-molded body of high density, when magnet material of thesame performance is used, the residual magnetization in particular canbe increased to result in an increase of a maximum magnetic energyproduct ((BH)_(max)). Further, due to a decrease of voids resulting froman increase of the density of the molded body, corrosion-resistance ofthe bond magnet can be increased. In particular, when the density of themolded body exceeds 6.1 ×10³ kg/m³ or more, magnetic properties such as(BH)_(max) can be further increased.

The density of the bond magnet is obtained by accurately measuring theshape thereof to obtain a volume and by measuring mass thereof with abalance of high precision. A surface portion of the bond magnet thereonrust preventive coating is applied has to be removed. Accordingly, bycutting into a shape by which accurate measurement of dimension can bedone, the cut out body can be evaluated. The measurement can be carriedout due to Archimedes's principle.

The magnet material used in the present bond magnet comprises rare earthelement-iron-nitrogen as main components and TbCu₇ phase as a principalcrystal phase. As such magnet material, for instance, one having acomposition expressed substantially by

General formula: {(R¹ _(X)R² _(1−X))_(Y)B_(Z)T_(1−Y−Z)}_(1−Q)N_(Q)  (1)

(in the formula, R¹ indicates at least one kind of element selected fromrare earth elements, R² at least one kind of element selected from Zr,Hf and Sc, T at least one kind of element selected from Fe and Co, andX, Y, Z and Q are numbers in terms of atomic ratio satisfyingrespectively 0.2≦X≦1, 0.04≦Y≦0.2, 0≦Z≦0.1, and 0.01≦Q≦0.2) andcomprising TbCu₇ crystal phase as the principal phase can be cited.

In the aforementioned formula (1), the R¹ element causes a largemagnetic anisotropy to the magnet material to result in high coerciveforce. As such R¹ elements, rare earth elements such as La, Ce, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y can be cited. Among these, inparticular more than 50% of the R¹ element is preferable to be Sm.Thereby, the magnetic anisotropy of the principal phase can be increasedto result in an increase of the coercive force.

The R² element is at least one kind of element selected from Zr, Hf andSc. Such R² element occupies mainly rare earth sites of the principalphase and has an effect to reduce an average atomic radius of the rareearth sites. Thereby, the TbCu₇ type crystal phase can be promoted togrow, and the concentration of Fe or Co in the TbCu₇ type crystal phasecan be increased. Further, the R² element, when manufacturing the magnetmaterial through quenching method or the like, promotes to becomeamorphous during quenching, further to be finer grains after heattreatment. These contribute in an improvement of magnetic properties.The R² element prevents α-Fe phase from precipitating in the magnetmaterial to result in showing also an effect of improving the magneticproperties.

In the formula (1), a sum Y of R¹ and R² elements is preferable to be inthe range of 0.04≦Y≦0.2, being more preferable to be in the range of0.05≦Y≦0.15. This is because due to a larger sum Y of R¹ and R² elementsa larger magnetic anisotropy can be obtained to result in giving highercoercive force. However, the R¹ and R² elements, when compounded toomuch, are likely to cause deterioration of the magnetization.

The ratio of the R¹ element to the sum of the R¹ and R² elements ispreferable to be in the range of 0.2≦X≦1. When the content of the R¹element is extremely reduced, the magnetic anisotropy decreasesremarkably to cause a difficulty in obtaining magnet material of largecoercive force. Accordingly, the ratio X of the R¹ element is preferableto be 0.2 or more. In addition, since the larger ratio X of the R¹element is advantageous in obtaining the higher coercive force, thevalue of X is preferable to be 0.5 or more. However, when the ratio ofthe R¹ element is made extremely large, α-Fe phase is caused toprecipitate. Accordingly, the value of X is preferable to be 0.95 orless. The value of X is more preferable to be in the range of0.65≦X≦0.85.

B (boron) is an element, due to making amorphous during quenching andmaking finer grains after heat treatment, effective in improvingresidual magnetization and preventing α-Fe phase from precipitating.Though an addition of B can bring about preferable properties, B is notnecessarily required to compound in the magnet material used in thepresent invention. When boron is compounded in excess, during the stepof heat treatment, R₂Fe₁₄B phase is conspicuously formed to be liable tocause a deterioration of magnetic properties of the magnet material.Accordingly, the content Z when the boron is added is preferable to be0.1 or less. Thus, the content Z of boron is in the range of 0≦Z≦0.1.The content of boron is more preferable to be in the range of0.001≦Z≦0.1, being further more preferable to be in the range of0.001≦Z≦0.05.

The T element is at least one kind of element selected from Fe and Co,having a function of increasing the saturation magnetization of themagnet material. The increase of the saturation magnetizationaccompanies an increase of the residual magnetization to result in anincrease of the maximum magnetic energy product. Such T element ispreferable to incorporate 70% or more in the magnet material, therebybeing able to effectively increase the saturation magnetization. Infurther increasing the saturation magnetization of the magnet material,the Fe content occupying in the total amount of the T element ispreferable to be 50 atomic % or more.

Part of the T element may be replaced by at least one kind of element(hereinafter referred to as M element) selected from Ti, Cr, Cu, Mo, W,Mn, Ga, Al, Sn, Ta, Nb, Si and Ni. By replacing the part of the Telement with such an M element, various characteristics important inpractical use such as corrosion resistance and heat resistance can beimproved. When the T element is extremely replaced by the M element,magnetic properties are remarkably deteriorated. Accordingly, an amountof replacement of the T element by the M element is preferable to be 20atomic % or less.

N (nitrogen) exists mainly in the interstices of the lattice of theprincipal phase to improve Curie temperatures and magnetic anisotropy ofthe principal phase in comparison with the case of nitrogen being notcontained. Among these, the improvement of the magnetic anisotropy isimportant in giving a large coercive force to the magnet material.Though a small amount of N exhibits an effect, when added in excess,α-Fe phase precipitates much. Accordingly, the content Q of the N ispreferable to be in the range of 0.01≦Q≦0.2, more preferable to be inthe range of 0.02≦Q≦0.2, further more preferable to be in the range of0.1≦Q≦0.2, still further more preferable to be in the range of0.11≦Q≦0.18.

Part of N can be replaced by at least one kind of element (hereinafterreferred to as X element) selected from C and P. Thereby, magneticproperties such as the coercive force can be improved. When an amount ofreplacement of N by the X element is too much, an effect of improvingthe Curie temperatures and the magnetic anisotropy of the principalphase is lowered. Accordingly, the amount of replacement of N by the Xelement is preferable to be 50 atomic % or less.

The magnet material substantially expressed by the formula (1) permitsto contain an avoidable impurity such as oxide or the like. Theprincipal phase (TbCu₇ type crystal phase) in the magnet materialindicates one of which volume ratio in constituent phases including anamorphous phase in an alloy is the largest. In the present invention,the principal phase is preferable to be contained 50% or more by volumeratio. Further, from a viewpoint of magnetic properties, the TbCu₇ typecrystal phase is preferable to be contained 80% or more by volume ratio.The crystal structure can be easily confirmed by use of X-raydiffraction or the like.

By the way, depending on the conditions of heat treatment forcrystallization that will be later described, a soft magnetic phase thatis substantially consisting of Fe or Co such as α-Fe phase mayprecipitate. However, the soft magnetic phase of fine grains of whichaverage grain diameter is for instance 50 nm or less contributes inimproving the residual magnetization. However, the ratio of the softmagnetic phase such as α-Fe phase is preferable to be 20% or less byvolume ratio. When the average grain diameter of the soft magnetic phaseexceeds 50 nm or the volume ratio of the soft magnetic phase exceeds 20%by volume ratio, the coercive force is remarkably lowered.

The present invention exhibits an effect in particular when flakes ofmagnet material of which thickness is less than 200 μm are used. Thatis, the flakes of magnet material of which thickness is less than 200 μmare large in spring back in manufacturing the bond magnet to beextremely difficult to sufficiently increase the density of the moldedbody due to the ordinary press forming. According to the presentinvention, the density of the bond magnet in which such flakes of magnetmaterial are used can be increased to such a high density as 6×10³ kg/m³or more with good reproducibility.

The flakes of magnet material of which thickness is less than 200 μm canbe manufactured by ejecting master alloy in for instance a molten stateonto a coolant to quench. That is, an alloy ingot or the like of whichcomposition is substantially expressed by

General formula: (R¹ _(X)R² _(1−X))_(Y)B_(Z)T_(1−Y−Z)  (2)

(in the formula, R¹ denotes at least one kind of element selected fromrare earth elements, R² at least one kind of element selected from Zr,Hf and Sc, T at least one kind of element selected from Fe and Co, andX, Y and Z are numbers in terms of atomic ratio satisfying respectively0.2≦B≦1, 0.04≦Y≦0.2 and 0≦Z≦0.1. Part of T element (for instance 20atomic % or less) may be replaced by at least one kind of M elementselected from Ti, Cr, Cu, Mo, W, Mn, Ga, Al, Sn, Ta, Nb, Si and Ni) isprepared by use of arc melting or high frequency melting.

Such master alloy, after melting, is ejected onto a coolant moving withhigh speed such as a single roll or a twin roll to quench. Thereby,flakes (or ribbon) of alloy material of which principal phase is TbCu₇type crystal phase, or flakes of alloy material that is made amorphousare manufactured. In the present invention, it is preferable, byapplying heat-treatment to the alloy material that is made amorphous inparticular to crystallize, to obtain the flakes of alloy material ofwhich principal phase is TbCu₇ crystal phase. According to such heattreatments, the grain diameter of the TbCu₇ type crystal phase can bemade finer and more homogeneous to result in enabling to improve themagnetic properties.

The aforementioned heat treatment is preferable to implement in anatmosphere of an inert gas for instance such as Ar or a vacuum under theconditions of a temperature in the range of 300 to 1200° C. and a timeof 0.1 to 200 hours. In this case, depending on the conditions of heattreatment, the α-Fe phase may precipitate to cause deterioration of themagnetic properties. However, when the grain diameter of the softmagnetic phase such as the aforementioned α-Fe phase is sufficientlyfine, there is a chance where the magnetic properties can be improved onthe contrary.

Next, the aforementioned flakes of alloy material are heat-treated in anatmosphere containing nitrogen to nitride. Thereby, the flakes of magnetmaterial of which principal phase is the intended TbCu₇ type crystalphase can be obtained. The heat-treatment for nitriding is preferable toimplement in an atmosphere of nitrogen gas of 0.01 to 10 atmosphericpressure under a temperature of 400 to 500° C. The nitriding treatmentunder such conditions is preferable to implement for a time of 0.1 to300 hours.

The atmosphere during nitriding treatment, instead of nitrogen gas, canbe a nitrogen compound gas such as ammonia gas or the like. When theammonia gas is used, the rate of nitriding reaction can be increased. Atthis time, by using together such gases as hydrogen, nitrogen, argon orthe like, the rate of nitriding reaction can be controlled. Bypulverizing the aforementioned alloy material preceding the nitridingtreatment, the rate of nitriding reaction can be increased. However,excess pulverization brings about much fine powder to tend to causedeterioration of magnetic properties.

In the flakes of magnet material used in the present invention, anaverage diameter of grains of TbCu₇ type crystal phase is preferable tobe in the range of 5 nm or more and less than 50 nm. By making fine theTbCu₇ type crystal phase (grains), the magnet material of high residualmagnetization, high (BH)_(max) and high coercive force can be obtained.When the average grain diameter of the TbCu₇ type crystal phase is lessthan 5 nm, the coercive force of the magnet material decreases. On theother hand, when the average grain diameter is more than 50 nm, anincrease in the residual magnetization and resultant increase of(BH)_(max) can not be sufficiently obtained. The average grain diameterof TbCu₇ type crystal phase is further preferable to be in the range of10 to 45 nm.

An average grain diameter of a hard magnetic phase is obtained in thefollowing way. In a photograph (photograph of agglomerates of finegrains) of one field of view obtained by TEM observation, each grain ischecked whether it is a TbCu₇ type crystal phase or not. For each grainthat is confirmed to be TbCu₇ crystal phase, grain diameter thereof ismeasured. Among these grain diameters, with maximum and minimum values,an average grain diameter is obtained. Such measurements are implementedin ten fields of view to average these values to obtain an average graindiameter of hard magnet material. Instead, from the half-value width ofX-ray diffraction, by use of Scherrer's equation, the average graindiameter can be obtained. The average grain diameter of theaforementioned soft magnetic phase is obtained from a photograph of onefield of view obtained by TEM observation as identical with the case ofthe hard magnetic phase. After checking whether each grain is bcc phase(Fe or FeCo) or not, each grain that is confirmed to be the bcc phase ismeasured of the grain diameter. An average value is obtained byaveraging the minimum and maximum values of grain diameters. An area ofthe TbCu₇ type crystal phase or Fe or FeCo phase in one field of view isobtained by image processing to regard as an area ratio. The area ratiois taken in two or more fields of view, followed by averaging to obtaina volume %.

A thickness of the flake of magnet material obtained by the quenchingmethod such as mentioned above is made less than 200 μm. When thethickness exceeds 200 μm, the effect of the present invention can not befully exhibited but also the grain diameter of the TbCu₇ type crystalphase becomes coarse to cause deterioration of the magnetic properties.The thickness of the flake of magnet material is more preferable to be150 μm or less, being still further preferable to be in the range of 5to 50 μm. By adjusting the thickness of flakes as described above, thegrain diameter of the TbCu₇ type crystal phase can be made fine withreproducibility. In addition, the flake of magnet material of whichthickness is in the range of 5 to 50 μm is large in the spring back inmanufacturing in particular the bond magnet. Accordingly, the bondmagnet due to the present invention can be effectively densified.

The thickness of magnet material is measured in the following ways. Inone method, a sample of a thin ribbon obtained by quenching, aftermeasuring a width and length thereof, is measured of its mass tocalculate the thickness by use the previously measured density. In theother method, the thickness is obtained from a photograph of a crosssection of the bond magnet. The magnet material, when being in flakes,can be measured by use of a ballpoint micrometer. In this case,measurements are made at more than ten points and the obtained valuesare averaged to obtain the thickness. In particular, in a sample ofwhich thickness is relatively thin, for instance 100 μm or less, whenquenched with a single roll, both sides of a surface in contact with theroll and a freely solidified surface tend to remain in approximatelyflat. By evaluating of this portion, an accurate thickness can beobtained.

The aforementioned magnet material and binder are mixed, the mixturebeing compression-molded into a desired magnet shape to obtain a moldedbody constituting the present bond magnet. The binder used formanufacturing the bond magnet is not particularly restricted, ordinaryresin based binder or metal binder being used. The present invention isparticularly effective in the bond magnet that uses the resin-basedbinder.

For the resin-based binder, various kinds of resins such as for instanceepoxy-, nylon-, polyamide-, polyimide- or silicone-based resin can beused. In particular, epoxy-based resin is suitable. When heat resistanceis necessary, polyamide- or polyimide-based resin is preferably used.Though the resin being used can be in any form of powder, liquid ormixture thereof, in particular the liquid resin is preferably used toobtain the high density. The viscosity of the liquid resin is preferableto be in the range of 1 to 500 poise.

The aforementioned resin-based binder is preferable to be contained inthe range of 0.5 to 5% by mass with respect to the magnet material. Whenan amount of the binder exceeds 5% by mass, the magnetic properties ofthe bond magnet deteriorates. When applying the manufacturing method ofthe bond magnet of the present invention, only a small amount of bindercan sufficiently adhere between the magnet materials to enable to obtainthe bond magnet of necessary strength. However, when the amount ofbinder is less than 0.5% by mass, the magnet materials are liable to bepoorly adhered. The amount of the binder is preferable to be in therange of 1 to 3% by mass, being more preferable to be in the range of1.5 to 2.5% by mass.

To the present bond magnet, titanate-, silane-based coupling agent orthe like can be added. The coupling agent improves dispersion of powderto be effective in an increase of the density of magnet. When thesurface of the magnet powder is treated by lubricant such as fatty acid,salts of fatty acid, amines, or the like, the aforementioned spring backis suppressed to contribute in an improvement of the density of the bondmagnet. Further, with respect to an improvement of the density of thebond magnet, it is effective to give an appropriate distribution to theparticle diameter of magnet powder.

In the present bond magnet, the density of molded body of 6×10³ kg/m³,further that exceeding 6.1×10³ kg/m³ is realized based on themanufacturing method described later in detail. The shape of the bondmagnet also affects on the density of the molded body. Accordingly, inthe present bond magnet, the shape shown in the following is preferableto apply. Thereby, the aforementioned density of molded body can berealized with reproducibility.

That is, a ring of bond magnet 1 as shown in FIG. 1 is preferable to bean external diameter d1 of 30 mm or less, an internal diameter d2 of 0.1mm or more and a height h of 20 mm or less. The external diameter d1 ismore preferable to be 20 mm or less. Further, a thickness t of the ringportion is preferable to be 6 mm or less. The thickness t is morepreferable to be 4 mm or less. As to the relationship between thethickness t and height h, a shape of which ratio thereof (h/t) is in therange of 0.1 to 20 is preferable. According to such a ring, the flakesof magnet material of which thickness is less than 200 μm (inparticular, of a thickness of 5 to 50 μm) spring back with difficulty.Accordingly, the bond magnet is densified with ease.

The ring of bond magnet can be, other than one of which thickness isconstant, one of which thickness is uneven. As such a shape, forinstance, one of which external diameter side is circular and internaldiameter side is polygonal (for instance, hexagonal) can be cited.Further, a cross section of the bond magnet may be formed in amultistage in a direction of height.

In a planar bond magnet 2 as shown in FIG. 2, a thickness (a thicknessof a plate) T is preferable to be 6 mm or less, being more preferable tobe 4 mm or less. With such a shape, the flakes of magnet material can beeffectively suppressed from causing the spring back. A specific shape ofthe planar bond magnet may be formed circular or rectangular. Anexternal length D (a length of a diagonal in case of being a rectangularplate) of a disc of bond magnet is not particularly restricted. However,as identical with the case of being a ring, a shape of which ratiobetween the thickness T and the external length D (D/T) is in the rangeof 0.1 to 20 is preferably selected. The preferable external length D ofthe disk of bond magnet is 25 mm or less.

Next, modes for implementing the manufacturing methods of bond magnetsof the present invention will be described.

First, the magnet material and resin-based or metal binder describedabove are mixed. The magnet material is usually used afterpulverization. When being already pulverized during a manufacturing stepof the magnet material, the above step can be omitted. As theresin-based binder, the aforementioned various kinds of binders can beused. The compounding amount of the binder is as mentioned above. Whenthe metal bond magnets are manufactured, for the binder, low-melt metalor low-melt alloy is used. As specific examples of the metal binder, Al,Pb, Sn, Zn, Cu, Mg, Ga and alloys including these can be cited.

Here, as the magnet material thereto the present manufacturing methodscan be applied, first of all the magnet material of which principalphase is the aforementioned TbCu₇ type crystal phase can be cited. Thepresent manufacturing method, however, without restricting thereto, canbe applied to Nd—Fe—B system magnet material or also to rare earthsystem magnet materials of which principal phase, other than TbCu₇ typecrystal phase, is one of for instance Th₂Ni₁₇, Th₂Zn₁₇ and ThMn₁₂ typecrystal phases. These magnet materials can be obtained by controllingfor instance the composition in the aforementioned formula (1) orconditions of manufacturing the magnet materials.

In addition, the shape of the magnet material is neither necessarilyrestricted. The present manufacturing method, without restricting to theflake of magnet material, can be applied to powder or cake of magnetmaterial. From a viewpoint of removing a factor that reduces the densitydue to the spring back to attain densification of the bond magnet, it isparticularly effective when the flake of magnet material of whichthickness is less than 200 μm is used. Further, when the flake of magnetmaterial of a thickness of 5 to 50 μm that is large in spring back isused, the present invention exhibits more larger effects.

Next, the mixture of the aforementioned magnet material and binder iscompression molded into a desired magnet shape to obtain a compressionmolded body constituting the bond magnet. The compression molding of themixture is implemented by use of a press machine for forming. In thiscase, one of the condition controls shown in the following (A) to (C) isapplied. A combination thereof can be applied. By implementing the presscontrols shown in (A) to (C), the density of the bond magnet can beeasily densified with reproducibility.

(A). Pressure is applied a plurality of times to the mixture of themagnet material and binder.

(B). In compression-molding the mixture of the magnet material andbinder, with at least one selected from a punch and a die rotating orreciprocating, the pressure is applied to the mixture.

(C). In compression-molding the mixture of the magnet material andbinder, while applying the pressure to the mixture, the binder is cured.

First, the control of the press conditions of (A) will be explained indetail. That is, in the step of press forming the mixture of the magnetmaterial and binder, between a maximum pressure and a pressure that is90% or less of the maximum pressure, compression and decompression tothe mixture are alternately repeated a plurality of times. In morespecific, in the step of press forming the mixture, with the proceduresof (a) and (b) shown in the following as one step, this step ispreferably repeated twice or more.

(a). Pressure of 6×10² MPa or more (P₁: a maximum pressure) is appliedto the mixture of the magnet material and binder.

(b). Subsequently, the pressure is lowered to the pressure (P₂) that islower by 2×10² MPa than the maximum pressure P₁ that is applied in (a).

That is, after the maximum pressure (for instance, pressure P₁ of 6×10²MPa or more) is applied to the mixture, the pressure is once lowered to90% or less of the maximum pressure, further to the pressure P₂(≦P₁−2×10² MPa). In other words, in the course of the step of pressforming, the pressure is released a certain degree. Thereby, thefriction or spring back between the magnet materials that hindersdensification can be cancelled. Thereafter, the maximum pressure P₁ isapplied again, thereby enabling to apply effective pressure to themagnet material. Through such operations, the magnet material isappropriately broken to enable to realize densification of the bondmagnet.

The maximum pressure P₁, though depending on the shape and kind of themagnet material, is preferable to be 6×10² MPa or more. When the maximumpressure P₁ is less than 6×10² MPa, the molded body may not besufficiently densified. The maximum pressure P₁ in the step of pressureapplication of (a) is more preferable to be 8×10² MPa or more.

On the other hand, in the step of pressure release of (b), the pressureis preferable to be lowered to that of 90% or less of the maximumpressure P₁. When the pressure during pressure release exceeds 90% ofthe maximum pressure P₁, the spring back cancellation effectaccompanying the pressure release can not be sufficiently obtained.During the step of pressure release, it is further preferable to lowerthe pressure by 2×10² MPa or more from the maximum pressure P₁.

The pressure P₂ in the step of pressure release is preferable to be2×10² MPa or less particularly in terms of an absolute value of thepressure. Thereby, an effect of cancellation of the friction and springback between magnet materials can be more effectively exhibited. Thepressure P₂ in the step of pressure release is preferable to beapproximately zero (state of atmospheric pressure) from a viewpoint ofimprovement of the density. In the present invention, however, theaforementioned step consisting of procedures of (a) and (b) is repeatedtwice or more. Accordingly, considering a shift towards the followingstep of pressure application, a certain degree of pressure is preferableto be maintained. Thereby, formability of the bond magnet can beprevented from lowering.

Number of repetition of the step consisting of (a) and (b) procedures isparticularly preferable to be five times or more. According to suchpress operations, the bond magnet that is further densified can beobtained with good reproducibility.

Next, the press condition control of (B) will be described in detail.That is, in a state where pressure is applied to the mixture of themagnet material and binder, a press mold (punch and die) is rotated soas to apply torsional stress to the mixture, or is reciprocated so as toapply shearing stress to the mixture. Thereby, the friction or springback between the magnet materials that is a factor hinderingdensification can be cancelled to enable to densify the bond magnet.

FIGS. 3 to 8 show specific constitutions of the control of pressconditions of (B), respectively. In these figures, reference numerals11, 12, 13, 14 and 15 denote the mixture (forming material of the bondmagnet) of the magnet material and binder, die, upper punch, lower punchand center punch, respectively.

For instance, in the step of press molding of the mixture 11, as shownin FIG. 3, the upper punch 13 is rotated, or as shown in FIG. 4, theupper and lower punches 13 and 14 are rotated in directions opposite toeach other. That is, the upper and lower punches 13 and 14 are rotatedrelatively with respect to a center axis so as to apply torsionalstress. Such a step of pressing is effective in forming a disk of magnetof a thickness of 6 mm or less (further 4 mm or less, still further 2 mmor less) and a ring of magnet of which thickness in a direction ofdiameter is larger than a height thereof.

As shown in FIG. 5, the die 12 and upper punch 13 (or the lower punch14) are rotated relatively with respect to the center axis so as toapply torsional stress. Such a step of pressing is effective in forminga disk of magnet of a thickness of 5 mm or less (further 3 mm or less,still further 1.5 mm or less), or a ring of magnet of which thickness ina direction of diameter is larger than the height.

Further, as shown in FIG. 6, the die 12 and the center punch 15 arerotated relatively with respect to the center axis so as to applytorsional stress, or as shown in FIG. 7, the upper punch 13 (or lowerpunch 14) and the center punch 15 are rotated relatively with respect tothe center axis so as to apply torsional stress. Such steps of pressingare effective in forming a ring of magnet of which thickness in adirection of diameter is smaller than the height thereof, or a cylinderof magnet.

As shown in FIG. 8, the die 12 and center punch 15 may be relativelyreciprocated in a direction parallel to the center axis. Such a step ofpressing is effective in forming a ring of magnet of which thickness ina direction of diameter is smaller than the height thereof or a cylinderof magnet.

An angle of rotation of the aforementioned punch or die needs only to beset at 1° or more. A rotation of 360° or more, that is a plurality ofrotations of the punch and die within a period of press is alsopermissible. During the press period, a direction of rotation of thepunch and die may be reversed to compress, followed by repetition offurther reversal. The control of press conditions of (B) exhibits afurther effect when combined with the control of conditions of (A).

Next, the control of press conditions of (C) will be described indetail. That is, in a state where the pressure is applied to the mixtureof the magnet material and binder, a temperature is raised up to onecapable of curing the resin used as the binder. Thereby, the lowering ofthe density due to the spring back or the like of the magnet materialcan be suppressed. The control of press conditions of (C) can becombined with the condition controls of (A) and (B) to use. Inimplementing as small as possible improvement of the press machine tosuppress an increase of manufacturing costs accompanying therewith, itis desirable to apply the controls of press conditions of (A) and (B).

In manufacturing the bond magnet of the present invention, means fordensifying the density are not restricted to the aforementioned controlsof press conditions of (A) to (C). Various kinds of methods capable ofsuppressing the spring back due to thinness of the magnet material canbe applied. For instance, by lengthening the press time of one step, thedensity of the bond magnet can be increased. In this case, though theconditions are set considering the pressure, the concrete press time ispreferable to be set between 5 seconds and 10 minutes, furtherpreferable to be between 10 seconds and 8 minutes. Due to such a longtime press step, even the magnet material around the center of themolded body is caused to break down to homogenize the pressuredistribution inside the molded body, resulting in an increase of thedensity of the molded body.

Further, the resin, when pressed in a state where a temperature in themold is raised up to a melting temperature (softening temperature) ormore of the resin based binder, is increased in its fluidity to enableto sufficiently transfer the pressure. Thereby, the spring back iscaused to occur with difficulty. For instance, powder of the magnetmaterial is compounded together with thermoplastic resin such as nylonsystem or polyethylene terephthalate to prepare a sample. The compoundedsample is molded under pressure in a state where the temperature in themold is raised up to the melting temperature of the resin or more.Thereafter, the sample is cooled in the mold to form a bond magnet ofhigh density. In this case, the powder of magnet material is preferableto be one in which particles of a length of 5 mm or less and of athickness in the range of 10 to 30 μm occupy 60% or more from aviewpoint of densification.

After filling the mixture of the magnet material and binder in theforming mold, by applying preceding the press forming supersonicvibration to densify a state inside the material, densification of themolded body can be accomplished. Further, means of pulverizing thepowder during compression molding, or means of applying instantaneousshock such as for instance in explosive forming can be applied todensify.

In the case of thermosetting resin such as epoxy-based resin being usedas the binder, after implementing the aforementioned step of compressionmolding, a step of curing is preferable to implement at a temperature ofapproximately 100 to 200° C.

According to the aforementioned manufacturing methods of the presentinvention, the bond magnet of high density can be manufactured withmagnet material of which principal phase is TbCu₇ type crystal phasethat is difficult to densify. That is, even in this case as mentionedabove, the density of molded body of 6.0×10³ kg/m³, further thatexceeding 6.1×10³ kg/m³ can be realized with reproducibility. That is,in the case of flake (or thin ribbon) of magnet material that isprepared through quenching being used, the aforementioned friction orspring back between magnet materials can be causes of hindrance indensification. However, according to the present manufacturing methods,these causes can be cancelled to enable a further improvement of thedensity of the molded body.

The present manufacturing methods of bond magnet, as mentioned above,can be applied to various kinds of magnet materials such as Nd—Fe—Bsystem magnet material and rare earth system magnet materials of whichprincipal phase is one of Th₂Ni₁₇, Th₂Zn₁₇, ThMn₁₂ type crystal phasesor the like. According to the present invention, the bond magnet usingvarious kinds of magnet materials can be densified. In particular, thepresent invention is effective in densifying the bond magnet that usesthe flake of magnet material of a thickness of less than 200 μm preparedby use of quenching method, further the flake of magnet material ofwhich thickness is in the range of 5 to 50 μm.

The present bond magnets or the bond magnets obtained by the presentmanufacturing methods can be used in various kinds of electricalappliances such as motors, measuring instruments or the like. Inparticular, these are suitable as components of various motors in whichsmaller size and higher performance are demanded. As examples, such asmedium driving spindle motors used in HDDs, FDDs, CD-ROMs and DVDs, lensactuators for light pick-ups, motors for printers, pager motors forvibration generation of such as portable telephones, and actuators forautomobile speed meters can be cited. The cylindrical bond magnets areeffective as thin, high performance speaker magnets of instruments thatare made thinner and lighter such as portable telephones.

An actuator of the present invention comprises the bond magnet of thepresent invention such as described above. FIG. 9 is a diagram showingone constitution example of a hard disk drive (HDD) that has a motor(spindle motor in specific) comprising a rotor (or stator) having thepresent bond magnet as a motor for driving a recording medium (magneticdisk).

A magnetic disk 21 is mounted to a spindle of a spindle motor 22. Thespindle motor 22 comprises a cylinder having the present bond magnet asfor instance a rotor, the spindle being fixed to the rotor. The bondmagnet constituting the cylinder is magnetized, along a direction of anarc thereof, in N and S poles in turn. Inside the cylinder anelectromagnet is disposed as a stator, by switching N and S poles of theelectromagnet the rotor being rotated due to an action of magneticforce. Together with the rotor the spindle rotates, thereby the magneticdisk 21 being rotated.

The bond magnet can be applied without restricting to the rotor. Withthe cylinder or the like having the present bond magnet as a stator, theelectromagnet may be used as a rotor. These are identical with theordinary motor structure.

A magnetic head for writing/reading information to and from the magneticdisk 21 is formed at the tip end of a head slider 23. The head slider 23is attached to the tip end of a thin film of suspension 24. Thesuspension 24 is connected to one end of an actuator arm 25. To theother end of the actuator arm 25, a voice coil motor 26 that is a kindof a linear motor is disposed.

The voice coil motor 26 is constituted of a not shown driving coil woundup to a bobbin portion of the actuator arm 25 and a magnetic circuitconsisting of a permanent magnet and counter yoke disposed facing toeach other so as to sandwich the driving coil. For these, the presentbond magnets can be applied. The actuator arm 25 is supported by ballbearings (not shown in the figure) disposed at two positions of aboveand below a fixed axis 27, being free in sliding/rotating due to thevoice coil motor 26.

The aforementioned spindle motor 22, due to the use of the present bondmagnet excellent in magnetic properties such as residual magnetizationand the maximum magnetic energy product as mentioned above, is realizedto be further smaller in size and further higher in performance.Further, by the use of such the spindle motor 22 as a driving motor ofthe magnetic disk 21, the HDDs or the like can be made smaller in sizeand higher in performance.

Next, specific embodiments of the present invention will be explained.

Embodiment 1

First, the respective raw materials of high purity are compoundedaccording to a prescription, being melted by high frequency in anatmosphere of Ar to prepare an ingot of master alloy. Next, the ingot ofmaster alloy is melted in an atmosphere of Ar by use of high frequencyinduction heating. The molten alloy is ejected from a nozzle onto acooling roll rotating with a peripheral speed of 45 m/s to quench,thereby a ribbon of alloy being prepared. A thickness of the ribbon is12 to 14 μm. The thickness is measured with a ballpoint micrometer.

Subsequently, the aforementioned ribbon of alloy is heat-treated in anatmosphere of Ar at a temperature of 760° C. for 60 minutes. Uponanalyzing the heat-treated ribbon of alloy by use of X-ray diffraction,with the except of only a small amount of diffraction peaks due to α-Fephase, all other peaks are confirmed to be capable of indexing to aTbCu, type crystal type structure. Next, the ribbon of alloy, afterbeing pulverized to flakes of an average grain diameter of approximately100 μm, is heat-treated in an atmosphere of nitrogen gas of 101 kPa (oneatmospheric pressure) under the conditions of 450° C.×50 hours, therebyforcing to absorb nitrogen to form magnet material.

The aforementioned magnet material, as a result of chemical analysis, isconfirmed to have a composition of Sm₇Zr₃Co₄B₁N₁₅Fe_(bal).({(Sm_(0.7)Zr_(0.3))_(0.12)B_(0.01)(Fe,Co)_(0.87)}_(0.85)N_(0.15)). Byobserving the magnet material with TEM, an average grain diameter of theprincipal phase and a volume ratio of the soft magnetic phase consistingof FeCo are investigated. As a result, the average grain diameter of theprincipal phase is 21 nm and the volume ratio of the soft magnetic phaseis approximately 5%.

To the magnet material thus obtained, 2% by mass of epoxy resin is addedas binder, followed by mixing. Thereafter, the mixture is set on ahydraulic press machine to implement compression molding after thefollowing procedures. First, (1) pressure of 10×10² MPa is applied.Subsequently, (2) the pressure is lowered to 0.5×10² MPa. The combinedprocedures of (1) and (2) are repeated five times. Thereafter, thepressure is decreased to zero to take out a molded body. The molded bodyis cured at a temperature of 150° C. for 2.5 hours to obtain an intendedbond magnet. The obtained bond magnet is measured of density, residualmagnetization, coercive force and maximum magnetic energy product. Theresults are shown in Table 1.

Further, as a comparative example of the present invention, with theexception of after the aforementioned mixture of the magnet material andbinder is formed (only one time application of pressure) under thepressure of 10×10² MPa, the pressure being reduced to zero to take outthe molded body, identical with the aforementioned embodiment 1, a bondmagnet is produced. The bond magnet of the comparative example 1 is alsomeasured of density, residual magnetization, coercive force and maximummagnetic energy product. The results are together shown in Table 1.

TABLE 1 Embodiment 1 Comparative Example 1 Density (kg/m³) 6.12 × 10³5.94 × 10³ Residual 0.79 0.77 Magnetization (T) Coercive Force 765 765(kA/m) Maximum Magnetic 101 95 Energy Product (kJ/m³)

As obvious from Table 1, the bond magnet of embodiment 1 possesses thedensity of 6.0×10³ kg/m³ or more. Accompanying this, compared with thebond magnet of Comparative example 1 using the same magnet material, theresidual magnetization and maximum magnetic energy product areincreased.

Embodiment 2

In the step of compression molding the aforementioned bond magnet ofembodiment 1, with the exception of repetition times of the procedures(1) and (2) being set at the numbers shown in Table 2, identical withembodiment 1, the bond magnets are produced respectively. Each bondmagnet is measured of the density. These results are shown together inTable 2.

TABLE 2 Number of Repetition of Combination of (1) and (2) Density(kg/m³) Comparative 1 5.94 × 10³ Example 2 Embodiment 2 2 6.02 × 10³ 36.06 × 10³ 5 6.12 × 10³ 10 6.19 × 10³ 15 6.22 × 10³

As shown in Table 2, as the number of repetition of the combinedprocedures of (1) and (2) is increased, the density of the bond magnetshows a tendency to increase. In particular, more than five times ofrepetitions can further improve the density of the bond magnet.

Embodiments 3 to 10, Comparative Example 3 to 4

In the identical way with embodiment 1, an ingot of Sm—Zr—(Fe, Co)—Bsystem master alloy is melted. Thereafter, the molten alloy is ejectedfrom a nozzle onto a cooling roll rotating with a peripheral speed of 35m/s to quench, thereby ribbons of alloy being produced. Thicknesses ofthe ribbons are 15 to 17 μm. Further, as comparative examples 3 and 4,ribbons of alloy of a thickness of 300 μm are produced with a rollperipheral speed of 1 m/s.

Subsequently, the aforementioned ribbons of alloy each is heat-treatedin an atmosphere of Ar at 700° C. for 30 minutes. The heat-treatedribbons of alloy, due to X-ray diffraction analysis, are confirmed forall diffraction peaks to be indexed to the TbCU₇ crystal structure.Then, these ribbons of alloy are heat-treated in a flow of gas mixture(ratio of amounts of flow: NH₃ : H₂=1:10) of NH₃ and H₂ under conditionsof 420° C.×3 hours to introduce nitrogen, thereafter being heat-treatedat the same temperature for two hours in an atmosphere of nitrogen toform magnet material.

The aforementioned magnet materials are confirmed due to chemicalanalysis to have compositions of{(Sm_(0.75)Zr_(0.25))_(0.100)(Fe_(0.8)Co_(0.2))_(0.885)B_(0.015)}_(0.84)N_(0.16)for embodiments and {(Sm_(0.75)Zr_(0.25))_(0.10)(Fe_(0.8)Co_(0.2))_(0.89)B_(0.01)}_(0.87)N_(0.13) for comparative examples Further, in themagnet material of embodiments, according to TEM observation, an averagegrain diameter of the principal phase is 25 nm.

To each magnet material thus obtained, 2% by mass of epoxy resin isadded as the binder, followed by mixing. Thereafter, the mixture is seton a hydraulic press machine to implement compression molding and curingwith the identical procedures with embodiment 1. Now, the number ofpressing is two and magnets are molded into shapes shown in Table 3respectively. The shapes of the magnet are adjusted by changing themold. Properties of the respective bond magnets are shown together inTable 3.

TABLE 3 Shape of Molded Body (mm) Height/ Density External InternalThick- of Magnet (BH) max Diameter Diameter Height ness (kg/m³) (MGOe)Embodiment 10.0 4.0 2.0 0.67 6.20 × 10³ 14.5 3 Embodiment 8.0 4.0 6.03.0 6.30 × 10³ 14.9 4 Embodiment 6.0 3.0 6.0 4.0 6.32 × 10³ 15.1 5Embodiment 5.0 2.5 6.0 4.8 6.30 × 10³ 15.0 6 Embodiment 4.0 2.0 6.0 6.06.40 × 10³ 15.4 7 Embodiment 2.0 1.0 4.0 8.0 6.45 × 10³ 15.7 8Embodiment 1.0 0.5 5.0 20.0 6.16 × 10³ 14.0 9 Embodiment 0.8 0.2 4.013.3 6.45 × 10³ 15.5 10 Compara- 15.0 5.0 5.0 1.0 6.41 × 10³ 9.9 tiveExample 3 Compara- 18.0 14.0 45.0 22.5 6.35 × 10³ 9.5 tive Example 4

As obvious from Table 3, the present bond magnets are confirmed to havelarge maximum magnetic energy products. The bond magnets of comparativeexamples 3 and 4, in spite of high densities thereof, show poorproperties as the bond magnet due to poor characteristics of the magnetmaterial.

Embodiments 11 to 19, Comparative Examples 5 to 8

In the identical way with embodiment 1, an ingot of Sm—Zr—(Fe, Co)—Bsystem master alloy, after being melted, is ejected onto a cooling rollrotating with a peripheral speed of 30 m/s to quench, thereby ribbons ofalloy of embodiments 11 to 16 being prepared. The thicknesses thereofare 18 to 20 μm. In addition, as comparative examples 5 to 8, in theidentical way except implementing with Sm—(Fe, Co) system master alloy,ribbons of alloy are prepared. Further, with a twin roll and aperipheral speed of 20 m/s, the molten alloy of the same compositionwith that of embodiments 11 to 16 is quenched to produce flakes of alloy(Embodiments 17 to 19) of a thickness of 45 μm.

Subsequently, ribbons of alloy and flakes of alloy each is heat-treatedin an atmosphere of Ar at 720° C. for 40 minutes. The heat-treatedribbons of alloy, due to X-ray diffraction analysis, are confirmed allthe diffraction peaks thereof can be indexed to TbCu₇ type crystalstructure. Then, the respective thin ribbons of alloy are heat-treatedin an atmosphere in which a ratio of flow rates of NH₃ and H₂ is 1:15under the conditions of 440° C.×3.5 hours to introduce nitrogen,followed by heat-treatment at the same temperature for two hours in anatmosphere of nitrogen to prepare magnet materials.

The aforementioned magnet materials, due to chemical analysis, areconfirmed to have a composition of{(Sm_(0.8)Zr_(0.2))_(0.10)(Fe_(0.8)Co_(0.2))_(0.88)B_(0.02)}_(0.85)N_(0.15).The magnet materials of the comparative examples are confirmed to have acomposit ion of {(Sm_(0.10)(Fe_(0.9)Co_(0.1))_(0.90)}_(0.87)N_(0.15).Average grain diameters of the principal phases of embodiments 11 to 16obtained from half-widths of X-ray diffraction patterns are 30 nm, thoseof embodiments 17 to 19 being 45 nm.

To each magnet material thus obtained, 2% by mass of epoxy resin isadded as the binder, followed by mixing. Thereafter, the mixture is seton a hydraulic press machine to compression-mold and cure as identicalwith the procedures of embodiment 1. In this case, the number ofpressing is twice and the shapes of the magnets are as shown in Table 4.The shape of the magnet is adjusted by changing the mold. The propertiesof the respective magnets are shown together 5 in Table 4.

TABLE 4 Shape of Molded Body External Density of Diameter Height Magnet(BH) max (mm) (mm) (kg/m³) (MGOe) Embodiment 16 1.5 6.35 × 10³ 14.5 11Embodiment 25 2.5 6.43 × 10³ 14.9 12 Embodiment 10 1.0 6.48 × 10³ 15.113 Embodiment 8 1.0 6.45 × 10³ 15.0 14 Embodiment 5 1.0 6.52 × 10³ 15.415 Embodiment 3 1.0 6.45 × 10³ 15.0 16 Embodiment 10 1.0 6.50 × 10³ 14.717 Embodiment 5 1.0 6.48 × 10³ 14.5 18 Embodiment 3 1.0 6.52 × 10³ 14.819 Comparative 30 5.0 5.91 × 10³ 11.0 Example 5 Comparative 30 10.0 5.85× 10³ 8.8 Example 6 Comparative 25 5.0 5.95 × 10³ 9.2 Example 7Comparative 30 0.5 5.68 × 10³ 8.0 Example 8

As obvious from Table 4, the present bond magnets are confirmed to havelarge maximum magnetic energy products. On the other hand, the bondmagnets of comparative examples 5 to 8 are confirmed to be poor inproperties.

Embodiments 20 to 23

In the identical way with embodiment 1, an ingot of Sm—Zr—(Fe, Co)—Bsystem master alloy is melted. Thereafter, the molten alloy is ejectedfrom a nozzle onto a cooling roll rotating with a peripheral speed of 40m/s to quench, thereby ribbons of alloy being produced. Thicknesses ofthe ribbon are 14 to 16 μm.

Subsequently, the aforementioned ribbons of alloy each is he at-treatedin an atmosphe re of Ar at 700° C. for 60 minutes. The heat-treated thinribbons of alloy, due to X-ray diffraction analysis, are confirmed alldiffraction peaks can be indexed to the TbCu₇ crystal structure. Then,these ribbons of alloy are heat-treated in an atmosphere in which aratio of flow rates of NH₃ and H₂ is 1:20 under conditions of 440° C.×4hours to introduce nitrogen, thereafter being heat-treated at the sametemperature for two hours in an atmosphere of nitrogen to form magnetmaterials.

The aforementioned magnet materials are confirmed due to chemicalanalysis to have a composition of{(Sm_(0.65)Zr_(0.35))_(0.400)(Fe_(0.8)Co_(0.2))_(0.885)B_(0.015)}_(0.87)N_(0.13).Further, from TEM observation, an average grain diameter of theprincipal phase is confirmed to be 18 nm.

To each magnet material thus obtained, 2% by mass of epoxy resin isadded as the binder, followed by mixing. Thereafter, the mixture is seton a hydraulic press machine to implement compression molding accordingto the following procedures. Then, the respective magnets, after curing,are measured of magnetic properties. The results are shown in Table 5.The shape of the molded body is a ring of an external diameter of 5 mm,an internal diameter of 2.5 mm, and a height of 3 mm.

Press conditions

Embodiment 20: With the pressure of 10×10² MPa, being pressed for 1minute.

Embodiment 21: With the pressure of 10×10² MPa, a die being rotated by360° in a minute.

Embodiment 22: With the pressure of 10×10² MPa, a die being rotated by180° in a minute.

Embodiment 23: With the pressure of 10×10² MPa, a punch repeating a 45°rotation and counter rotation three times a minute.

TABLE 5 Density of Magnet (kg/m³) (BH) max (MGOe) Embodiment 20 6.23 ×10³ 14.7 Embodiment 21 6.34 × 10³ 15.2 Embodiment 22 6.40 × 10³ 15.6Embodiment 23 6.45 × 10³ 15.9

As obvious from Table 5, the present bond magnets are confirmed to havehigher densities and larger maximum magnetic energy products.

Embodiment 24

To magnet material prepared under the identical conditions withembodiment 1, 2% by mass of epoxy resin is added as the binder, followedby mixing. The mixture is set on a hydraulic press machine having amechanism that rotates the upper punch 13 and lower punch 14 shown inFIG. 4.

Then, while gradually applying pressure onto the mixture 11 with a speedof 1×10² MPa a minute, as shown in FIG. 4, the upper and lower punches13 and 14 are rotated reciprocating in the directions opposite to eachother. At a point of time when the pressure of 2×10² MPa is reached, theupper and lower punches 13 and 14 are stopped rotating to apply pressureof 10×10² MPa. The compression-molded body is taken out, followed bycuring in standard way. The density thereof is 6.21×10³ kg/m³. Themolded body has a shape of an external diameter of 16 mm and a thicknessof 1.5 mm.

As a comparative example of the present invention, with the onlyexception of not rotating the upper and lower punches 13 and 14 duringpressing, in the identical way, the bond magnet is produced. The densityof the molded body of the bond magnet is 5.73×10³ kg/m³.

Embodiment 25

To magnet material prepared under the identical conditions withembodiment 1, 2% by mass of epoxy resin is added as the binder, followedby mixing. The mixture is set on a hydraulic press machine having amechanism that rotates the upper punch 13 shown in FIG. 5.

Then, while gradually applying pressure onto the mixture 11 with a speedof 1×10² MPa a minute, as shown in FIG. 5, the upper punch 13 is rotatedreciprocating with respect to the die 12. At a point of time when thepressure of 2×10² MPa is reached, the upper punch 13 is stopped rotatingto apply pressure of 10×10² MPa. The compression molded body is takenout to cure in standard way. The density thereof is 6.09×10³ kg/m³. Themolded body has a shape of an external diameter of 20 mm, an internaldiameter of 18 mm and a thickness and height of ring portion of 1.5 mmand 5 mm, respectively.

As a comparative example of the present invention, with the onlyexception of not rotating the upper punch during press, in the identicalway the bond magnet is produced. The density of the molded body of thebond magnet is 5.75×10³ kg/m³.

Embodiment 26

To the magnet material prepared under the identical conditions withembodiment 1, 2% by mass of epoxy resin is added as the binder, followedby mixing. The mixture is set on a hydraulic press machine having amechanism that rotates the center punch 15 shown in FIG. 6.

Then, while gradually applying pressure onto the mixture 11 with a speedof 1×10² MPa a minute, as shown in FIG. 6, the center punch 15 isrotated reciprocating with respect to the die 12. At a point of timewhen the pressure of 2×10² MPa is reached, the center punch 15 isstopped rotating to apply pressure of 10×10² MPa. The compression-moldedbody is taken out to cure in standard way. The density thereof is6.05×10³ kg/m³. The molded body has a ring shape of an external diameterof 5 mm, an internal diameter of 2 mm and a thickness and height of thering portion of 1.5 mm and 5 mm, respectively.

As a comparative example of the present invention, with the onlyexception of not rotating the center punch during press, in theidentical way the bond magnet is produced. The density of the moldedbody of the ring of bond magnet is 5.51×10 kg/m³.

Embodiment 27

To magnet material prepared under the identical conditions withembodiment 1, 2% by mass of epoxy resin is added as the binder, followedby mixing. The mixture is set on a hydraulic press machine having amechanism that reciprocates up and down the center punch 15 shown inFIG. 8.

Then, while gradually applying pressure onto the mixture 11 at a speedof 1×10² MPa a minute, as shown in FIG. 8, the center punch 15 isreciprocated in a direction parallel with a central axis. At a point oftime when the pressure of 3×10² MPa is reached, the center punch 15 isstopped moving to apply the pressure of 10×10² MPa. Thecompression-molded body is taken out to cure in standard way. Thedensity thereof is 6.30×10³ kg/m³. The molded body has a cylinder shapeof an external diameter of 3 mm, an internal diameter of lmm, athickness of lmm and a height of 10 mm.

As a comparative example of the present invention, with the onlyexception of not reciprocating the center punch during press, in theidentical way a ring of the bond magnet is produced. The density of themolded body of the ring of bond magnet is 5.63×10³ kg/m³.

Embodiment 28

To the magnet material prepared under the identical conditions withembodiment 1, 2% by mass of epoxy resin is added as the binder, followedby mixing. The mixture is set on a hydraulic press machine to applypressure of 10×10² MPa. While maintaining the applied pressure, thetemperature of an entire mold is raised up to a curing temperature ofthe resin to cure. After cooling, the bond magnet is taken out tomeasure the density, the density being 6.25×10³ kg/m³.

As a comparative example of the present invention, without raising thetemperature of the mold during press, the molded body is taken out tocure in the standard way, thereby a bond magnet is produced. The densityof the molded body of the bond magnet is 5.63×10³ kg/m³.

Embodiment 29

To magnet powder (Sm—Zr—(Fe, Co)—B—N system magnet powder) preparedunder the identical conditions with embodiment 3, 15% by mass of nylon12 is added as the binder to kneed, compound being prepared. In themagnet powder, particles of a length of 5 mm or less occupies 70% byvolume, an average thickness being 17 μm. These values are obtained bysieving and calculation based on weights.

The aforementioned compound is put in a mold of a hydraulic pressmachine, the temperature of the mold is set at 220° C., and pressure of500 MPa is applied. While maintaining the applied pressure, the entiremold is cooled to the room temperature, thereafter the bond magnet istaken out from the mold. The shape of the magnet is an external diameterof 5 mm, an internal diameter of 2 mm and a height of 6 mm. The densityof the obtained bond magnet is 6.40×10³ kg/m³, (BH)max being 15.4 MGOe.

As obvious from the aforementioned embodiments, according to the presentinvention, even in the case of the magnet material of which principalphase is TbCu₇ type crystal phase being used, the bond magnet of whichdensity of molded body is densified to 6×10³ kg/m³ or more can beobtained with good reproducibility. That is, the bond magnet excellentin magnetic properties such as the maximum magnetic energy product orthe like and in corrosion resistance can be provided with goodreproducibility.

While the present invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in forms and detail maybe made therein without departing from the spirit, scope and teaching ofthe invention. Accordingly, the invention herein disclosed is to beconsidered merely as illustrative and limited in scope only as specifiedin the appended claims.

What is claimed is:
 1. A bond magnet, comprising: a molded body in whicha mixture including magnet material of which main component is rareearth element-iron-nitrogen and a binder is formed into a shape ofmagnet; wherein the magnet material comprises TbCu₇ type crystal phaseas a principal phase and a shape of flake of a thickness of less than200 μm, the molded body having a density of 6×10³ kg/m³ or more.
 2. Thebond magnet as set forth in claim 1: wherein the molded body has adensity exceeding 6.1×10³ kg/m³.
 3. The bond magnet as set forth inclaim 1: wherein the flake of magnet material consists of materialobtained by incorporating nitrogen in a ribbon of alloy consisting of aquenched body of molten alloy, and a thickness of the flake is in therange of 5 to 50 μm.
 4. The bond magnet as set forth in claim 1: whereinthe TbCu₇ type crystal phase has an average grain diameter of 5 nm ormore and less than 50 nm.
 5. The bond magnet as set forth in claim 1:wherein the molded body has a shape of ring, the ring being an externaldiameter, an internal diameter and a height of 30 mm or less, 0.1 mm ormore and 20 mm or less, respectively.
 6. The bond magnet as set forth inclaim 5: wherein the ring has a thickness of 6 mm or less in a directionof diameter.
 7. The bond magnet as set forth in claim 1: wherein themolded body has a planar shape, a thickness thereof being 6 mm or less.8. The bond magnet as set forth in claim 7: wherein the planar moldedbody has a shape of disk, an external diameter thereof being 25 mm orless.
 9. The bond magnet as set forth in claim 1: wherein the magnetmaterial has a composition substantially expressed by a general formula:{(R¹ _(X)R² _(1-X))_(Y)B_(Z)T_(1-Y-Z)}_(1-Q)N_(Q) (in the formula, R¹indicates at least one kind of element selected from rare earthelements, R² at least one kind of element selected from Zr, Hf and Sc, Tat least one kind of element selected from Fe and Co, and X, Y, Z and Qare numbers in terms of atomic ratio satisfying respectively 0.2 ≦X≦1,0.04≦Y≦0.2, 0≦Z≦0.1, and 0.01≦Q≦0.2).
 10. The bond magnet as set forthin claim 9: wherein 50 atomic % or more of the R¹ element is Sm.
 11. Thebond magnet as set forth in claim 9: wherein 50 atomic % or more of theT element is Fe.
 12. The bond magnet as set forth in claim 1: whereinthe mixture contains resin based binder as the binder.
 13. The bondmagnet as set forth in claim 12: wherein the mixture contains the binderin the range of 0.5 to 5 % by mass with respect to the magnet material.14. The bond magnet as set forth in claim 1: wherein the molded bodyconsists of a compression molded body of the mixture.
 15. The bondmagnet as set forth in claim 1, wherein the thickness of the flake is150 μm or less.
 16. The bond magnet as set forth in claim 1, wherein thebond magnet is located in an actuator.
 17. The bond magnet as set forthin claim 1, wherein the bond magnet is made by a method comprisingcompression molding a mixture of magnet material and binder into adesired magnet shape, wherein the pressure is applied a plurality oftimes to the mixture during the step of compression molding.
 18. Thebond magnet as set forth in claim 1, wherein the bond magnet is made bya method comprising compression molding a mixture of magnet material andbinder into a desired magnet shape, wherein at least one of a punch anddie for compression molding is rotated or reciprocated during the stepof compression molding.
 19. The bond magnet as set forth in claim 1,wherein the bond magnet is made by a method comprising compressionmolding a mixture of magnet material and binder into a desired magnetshape, wherein the binder is cured while applying pressure to themixture during the step of compression molding.